Method of providing ferrous articles with phosphate coatings and compositions therefor



United States Patent METHOD OF PROVIDING FERROUS ARTICLES WITH PHOSPHATE COATINGS AND COMPOSI- TIONS THEREFOR John A. Henricks, Logansport, Ind. (742 N. Oak Park Ave., Oak Park, Ill.)

N0 Drawing. Filed Jan. 22, 1957, Ser. No. 635,130 2 Claims. (Cl. 148-6.15)

This invention relates to the formation of integral phosphate coatings on metallic surfaces. More particularly, it relates to phosphate coating baths for forming on metallic surfaces improved phosphate coatings which are characterized by having a micro-crystalline or amorphous-like structure. 7

The almost universal practice in the automotive and appliance industries is to form a zinc, iron, or manganese phosphate coating on the surfaces of ferrous metals which are to be painted or enameled, drawn, adhered to or otherwise fabricated. The phosphate coating baths in general use form an integral phosphate coating which consists of many relatively large, elongated crystals. In contrast, the phosphate coating baths of the present invention form an integral phosphate coating which 'consists of a multiplicity of line, interlaced microcrystalline grains as will be hereinafter described.

Phosphate coating baths are prepared by dissolving phosphoric acid-and/or dihydrogen phosphate salt mixtures in water together with oxidizers and other additives to form a concentrate and then diluting the concentrate with Water to form a coating bath which is nearly saturated with the phosphate salt. The baths are heated to temperatures of from 110 to 200 F. and the work is dipped in the bath or is sprayed with the bath so as to form a phosphate coating on it.

The bath will coat only so long as it is maintained withincertain rangesof acidity, phosphate content, free acid content, etc. or, in other words, is in balance. The conventional means of analyzing baths to keep them in balance is to determine the specific gravity, free acid and total acid. The free acid is determined by titrating a 10 ml. sample of the solution to a bromphenol blue end point with N/ 10 sodium hydroxide. The total acid, or points, is determined by titrating a 10 ml. sample of the solution to a phenol phthalein end-point with N/ 10 sodium hydroxide. V

One way in which phosphate coating baths are made up is to prepare a dry mixture of suitable chemicals and pour the mixture into a tank of water to form a coating bath. However, difiiculty is encountered in storing these dry compositions in commercially used containers due to the deliquescent nature of the chemicals, particularly zinc nitrate and calcium chloride, which leads to the formation of a mushy, partially fused mass inside the container. i I I In'the fabrication of metals where a high gloss finish is desirable a fine crystal or amorphous phosphate coating has distinct advantages. The preparation of such a phosphate coating has been an exceedingly diflicult problem and in general the industry has had to accept relatively large crystal phosphate coatings where phosphate flakes off the metal when it is bent or flexed.

One object of the present invention isto provide phosphate coating baths and methods of compounding them so as to form integral microcrystallline or amorphous phosphate coatings on metallic surfaces which will permit P Cg 2,975,082

Patented Mar. 14, 1961 excessive bending or flexing of the phosphated metal without the flaking off of the coating.

Another object of the present invention is to provide a powder make-up composition for phosphate coating baths which remains relatively dry and free flowing even though stored for long periods of time. 7

Another object of the present invention is to provide phosphate coating baths which form integral microcrystalline phosphate coatings on metallic surfaces and which are readily operable in production in that they coat within a reasonable time, can be kept in balance without difficulty and are otherwise easy to handle.

Other objects and advantages will become apparent from the following description of the present invention.

I have found that when certain metallic ions such as the calcium ion and an accelerating agent such, for example, as a nitrate or nitrite are added in regulated quantities to aqueous acidic zinc, iron, or manganese phosphate coating baths, the baths form an improved micro crystalline or amorphous phosphate coating.- 1 have further found that, in order to maintain an operable bath, the metallic ions, accelerating agent, and phosphate ions have to be present in certain critical ratios.

The compositions prepared in accordance with this invention arepreferably based upon nitrate depolarized formulations prepared from phosphoric acid or highly soluble phosphates and highly soluble salts of zinc in prounit of zinc salts to four units of phosphoric acid. In the simplest of such formulations, the zinc is all incorporated as zinc nitrate but the desired zinc saturation may also be .secured by providing at least a part of the zinc in the I 1 form of iinc chloride with the range of balance being from 10 units of zinc nitrate to 1 unit of zinc chloride,

in a high nitrate formulation, to 1 unit of zinc nitrate to 3 units of zinc chloride, in low nitrateformulations. The chloride acts to improve the non-sludging charact6IlStlCS-0f the bath and also effects coating at a faster rate than baths which have all of the zinc in the form of the. nitrate. Ammonium yielding substances may also be incorporated, as for example, by employing am-* monium phosphate directly in the preparation .of the composition or by utilizing other substances therein which will facilitate the production of the ammonium radical. v

In the above ratios and other critical values which may be found herein in which zinc is conveniently used asthe principal coating ion, iron and. manganese may be substituted for the zinc when the former ions are used as the f Also, the principal coating one or more of the above principal coating cation. cation may be a mixture of ions.

gen phosphate, etc. Broadly, thecalciummay be intromental to the coating-forming ability of'the solutio The'preferred calcium to zinc ratio is fromabout l) While the calcium ion is preferred as the f6 The desired calcium content may be obtained byadding I. calcium to the solution, or to a concentrated makeup ma ten'al, in a variety of its available" forms including cium oxide, calcium hydroxide, calcium nitrate, calcium V chloride, calcium hydrogen phosphate, calcium dihydr'm producing the amorphous coatings of the present invention, an ion from a member of the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium and barium may be used to obtain a substantial portion of the benefits obtainable with'the calcium ion. These ions are preferably added in the form of their nitratesalt although other soluble salts may' also be used.

In order to coat within a reasonable time and overcome the positioning effect of the modifier, the coating baths of the present invention may contain nitrogen oxide depolarizer in the form of conventionally employed ac celerating or oxidizing agents such as a hydrogen or alkali metal nitrate, nitrite or chlorate, nitrosyl chloride or the like. The preferred oxidizing agent is one containing nitrogen oxide, is. a nitrogen oxide depolarizer such as a nitrate or nitrite.

Taking nitrate as the most representative member of the class of nitrogen oxide depolarizer or oxidizing agents that may be used, the ratio by weight of nitrate to phosphate, (NO /PO may extend from .16 to about 10.0 when the proportions and ratios of calcium and zinc above given are observed and best results are obtained when the ratio is about 1 to 4. A suitable amount of nitrate is readily determined by adding it to a coating bath until satisfactory coating action is obtained. The actual amount of nitrate in the preferred compositions of the present invention generally works out to be about 0.5 to 48 grams per liter. Other oxidizing agents may be used instead of nitrate, but when used should be employed in amounts which will produce approximately equivalent amounts of oxidizing or acceleration of coating formation. When chlorate is used, the ratio of ClO to P is preferably from about .07 to about 1.8; for nitrite, the ratio of N0 to P0 may extend from about 0.003 to about 0.1 and is preferably about 0.015 to .04; for hydrogen peroxide, the preferred ratio may extend from about .003 to 0.01 and for dinitrobenzene sulfonate the preferred ratio may extend from about 0.15 to 1.0. Other oxidizing agents such as bromates, iodates, pieric acid, t-butyl hydroperoxide, quinones, etc. may be used, if desired, in quantities which produce an effect on the coating formation equivalent to that which is produced by the above specified range for nitrate. Mixtures of oxidizing agents may be used, if desired, with the desired quantity being that which produces an effect on the coating equal to the effect obtained from the use of nitrate in quantities as previously stated.

When the oxidizing agent is one other than nitrate it is to be understood that it may be necessary to incorporate a quantity of an additional anion that is substantially innocuous to the coating or coating forming ability of the solution, such as chloride, to effectively maintain the ionic balance of the solution. Instead of supplementing the need for anions with chloride or other innocuous anion it may be desirable to introduce all or part of the calcium as calcium nitrate.

While oxidizing agents are generallyemployed as the accelerator, reducing agents such as sodium sulfite, hydrazine salts or solution, chloral hydrate or the like may also he used as the accelerating agents.

The resulting acceleration of the coating composition is such that complete coating of a metal surface can be effected in from 3 to 5 minutes with an immersion bath at a temperature in the order of 200 F. in contrast to the 30 minutes required for coating by a conventional zinc dihydrogen phosphate bath and minutes when conventional coating baths are modified by additions of zinc or sodium nitrate. Moreover, the coating produced from baths of the dihydrogen phosphate type, or those modified by the addition of zinc or sodium nitrate, are crystalline in nature while the coatings produced from baths to which a calcium salt or other modifier salt has been added, in at least the minimum quantities hereinafter specified, have a smooth texture exhibiting no visible crystal structure even when examined under magnification of diameters. Furthermore, the chemical analysis of these amorphous-type coatings, when zinc is the principal coating cation used, reveals that they are mixed phosphates with the metal of the recited group occurring therein in the ratio of about /2 mol thereof to each mol of zinc; the composition of the coating when lithium is used, for example, being Zn Li(PO Electronic diffraction analyses of the coatings indicates they are apatitlc in nature. Thus, such analysis of a coating produced on low carbon steel by a bath prepared in accordance with this invention and containing calcium and chlorine showed the coating to be microcrystalline or amorphous-like and have a diffraction pattern of an apatite with the pattern slightly distorted by the presence of zinc and iron.

A zinc phosphate coating bath is preferred in accordanee with the present invention since it appears that there is a co-deposit of calcium or other modifier cation and that the phosphate coating actually contains the calcium or other ion in addition to zinc.

The concentration of zinc in the diluted bath of the present invention is preferably in the range of about 1 to 4 grams per liter with the best results being obtained at a concentration of about 2.0 to 3.5 grams/liter. As is well known in the art, however, zinc phosphate coating baths may be made up that contain as low as concentration as /2 gram/liter and as high a concentration as 10 up to even 15 grams per liter.

The amount of phosphate used is enough so that ratio of zinc to phosphate is preferably from about 6.8 to 1 to about .17 to 1, with the best results being obtained with a ratio of about 3 to 1 to about 0.5 to 1.

The amount of phosphate in the preferred baths of the present invention works out to be generally from about .15 to 24 grams/liter with best results obtained with from about 0.5 to 12 grams/liter using the preferred amounts of zinc as previously discussed.

In accordance with the present invention, the amount of calcium present varies with the amount of zinc present. The preferred amount is, as previously stated, enough to keep the ratio of calcium ion to zinc ion in the range of about .5 to 4.5 by weight. There should be at least enough of the modifying cation (calcium) to maintain a ratio of it to the principal coating cation (zinc) of at least about .16 to 1 in order to obtain enough inhibiting action on the deposit of large crystals to obtain a satisfactory coating in accordance with the present invention. On the other hand, amounts of modifying cation which make a ratio of calcium to zinc larger than 10 to 1 prevent a satisfactory coating action. For most applications, the amount of calcium or other modifying cation in the diluted bath is preferably about .5 to 18 grams/liter as hereinafter described as the threshold value of the salt of modifying cation. When a ferrous metal surface has been thoroughly etched by acid pickling or the like, more of the modifying cation is required than when the surface is not as clean as, for example, when a surface of ferrous metal stock is treated that has been merely wiped with a solvent such as carbon tetrachloride.

Other salts may also be used in accordance with the present invention to give manganese or iron phosphate coatings. Manganese phosphate coatings are similar to zinc phosphate coatings in weight and composition and are as satisfactory except that they are more expensive and so not generally employed. Iron phosphate coatings are lighter in weight and are a mixture of iron oxides and iron phosphate. The are the least expensive of any coating and also the least satisfactory for many purposes although they do have special uses. In addition to forming an integral phosphate coating on iron and steel ferrous surfaces, baths of the present invention may also be used to coat zinc, aluminum, and many other metallic surfaces.

As mentioned above, the addition of a soluble salt of calcium, or other amorphous coating producing cation, to one of the nitrate or nitrogenoxide depolarized formulaapropos tions of the type mentioned, acts to accelerate the .coating rate and inhibit crystalline growth, the extent of crystalline inhibition depending upon the amount of additive metal employed.

There appears to be a minimum amountof a modifier such as calcium which must be added to the bath in order to substantially eliminate the crystalline structure. This amount may be defined as the threshold value vofgtho modifier and these values as determined for, commercial grade materials on clean metal panels employed in a broken-in, 25 point bath, compounded as in Example I below, containing approximately 3.2 grams per liter of zinc and approximately 0.5 gram per liter of iron, are substantially as follows:

A 20 to 30 point bath zinc dihydrogen phosphate is prepared by diluting, to a 2 to 3% by weight solution, a concentrate containing: I

Units, Formula Composition, Chemical WelghtXNo. 0! Percent by Mols Weight Phosphoric Acid HsPOq 98x0. 2 l9. 6 Mono-Ammonium Phosphate Zinc Chloride ZllCh. 136X0.1 13. 6

Zine Nitrate Zn (NO 189X0. 1 18. 9

Water added to dissolve salts 24. 9

This solution is then broken in and balanced to provide a 20 to 30 point bathby a trial load of ferrous articles thereby providing iron ions in the bath. To the balanced and broken-in bath there is added a nitrateof lithium, beryllium, magnesium, calcium, strontium, cadmium or barium in quantities approaching equimolarity so as to v be within the threshold values given above with the zinc. The bath is then ready for use and will befound to provide, a tight, microcrystalline coating.

The above specified threshold values are based, upon technical or commercial grade nitrates which contain traces of other metals as impurities. For example, the calcium, nitrate was found to have at least traces of strontium and magnesium. Lithium nitrate was found to have at least traces of aluminum, tin andstrontium; calcium nitrate contained traces of strontium, fluorine, iron, aluminum and magnesium; and barium nitrate contained traces of cerium, titanium and calcium: These trade impurities have'also been detected'inthecoatings by spectographic analysis and'they evidently have an auxiliary or synergist action in v inhibiting crystalline growth since the threshold concentrations of the modifier are materially less when employing commercial grades of the modifier material than when chemically pure grades of the modifiers are employed, While the above listed threshold values have been in zinc content from 1 to 4 grams per liter.

The required amount of the modifying metal. saltto I produce the amorphous coating may be reduced. by the additional smoothing effect of minor amounts of other materials. For example, the elementsknown as the amphoteric metals and which the central coordi vides adequate depolarization." 7

Although the addition of nitrates of lithium, beryllium, magnesium, calcium, strontium, cadmium or barium t0 nating atom in the formation of heteropoly acids, as is discussed in Inorganic Chemistry by Fritz Ephraim,

4th edition, pages500 to 509, may be so used. Of such elements, which include phosphorous, arsenic, antimony, boron, thorium, silicon, tin, cerium, titanium, cobalt, zirconium, iron, vanadium, aluminum, copper, manganese, chromium, iodine and germanium, those are pre ferred which do not form an immersion deposit on iron or do not tend to poison the bath by preventing depositit is presently preferred to simply employ commercial grade nitrates or other soluble salts of lithium, berylium, magnesium, calcium, strontium, cadmium, or barium thereby taking advantage of the trace impurities therein.

Likewise, the iron, acquiredin normal operation of commercial phosphating baths when coating ferrous surfaces, assists in the formation of the desired coating although the concentration of this iron should not exceed lgram per liter.

The iron concentration does not materially increase during normal, working of the bath with ferrous articles probably because of the oxidizing action caused by the air and by the interaction ofthe nitrate and chloride of the'zinc salts. However, in heavily worked baths, such as spray installations for ferrous articles where the iron concentration tends to increase, such increase may be controlled by the periodic addition of barium or sodium nitrite, or calcium hypochlorite, in amounts of less than 1 gram per liter. It should alsojbe mentioned that the aforementioned oxidation is solely for the purpose ofacceleration and reduction of ferrous'ironto thereby maintain a smooth amorphous coating through avoid-' ing the deposit of coarse iron phosphate crystals. There is no need to'efiect oxidization of hydrogen in baths compounded in accordance with this invention since the highcontent of .nitrate or its equivalent thereofpro;

a zinc orthophosphate composition has been heretofore described specifically with reference to a bath com pounded from a concentrate containing phosphoricacid,

mono-ammonium phosphate, zinc chloride and zinc nitrate in the proportions stated above, it is to be under'-- stood that baths compoundedfrom any of the formulations hereinafter set forth may be employed in similar manner.

' Example II.

It is also possible toadapt conventionalzinc dihydrogen phosphate compositions to production of amorphous mixed phosphate coatings by modifying the compositions" sothat'they are equivalent to ionized salt-based baths of, phosphoric acid, zinc nitrateand ammonium phosphate. Such modified composition in the form of a concentrate, may have the following constitutents:

Zinc dihydrogen phosphate concentrate (12% Ammonium nitrate 13.51 f

Water Composition, Percent by weight f I asraoaa This composition is prepared by dissolving anhydrous zinc chloride in the zinc dihydrogen phosphate concentrate. The ammonium nitrate is dissolved in the water and hydrochloric acid and the resulting solution is added to the cencentrate containing the zinc chloride. The resuiting composition is then chemically identical with the concentrate in Example I but is more dilute.

A more concentrated solution can be obtained by first warming the zinc dihydrogen phosphate solution, adding the hydrochloric acid thereto, and then dissolving the ammonium nitrate in the warm solution without additional water, and with the zinc chloride added as the final step. Similar results can be obtained by employing nitric acid and ammonium chloride to convert the zinc chloride, zinc phosphate solution to the desired chemical composition and it will be obvious that other chemicals may be utilized for this. A modifying metal nitrate such as calcium nitrate,'lithium nitrate and the like as listed in Example I is added to this bath after the other ingredients in at least the aforesaid minimum or threshold concentrations so as to provide a micro-crystalline phosphate coating.

Example III The first two examples described formulations for providing an amorphous mixed phosphate coating and disclosed the addition of the nitrate of the modifier metal after the other ingredients, provided in the form of a concentrate, had been diluted to substantially bath strength. However, the nitrate of the modifier metal may also be included as part of the concentrate as, for example: I

This concentrate was diluted to a 4% by volume solution, heated to 190200 F. and was employed asa coating bath for a wide variety of articles including ferrous automobile wheels and rims, low carbon steel tubing prior to drawing, and die-cast zinc hardware. The bath was maintained at a 20 to 30 point strength (or total acid strength) and had a ratio of total to free acid of between 5-10 to 1. Coatings were produced by immersion of the cleaned work in the bath for a period of 4 to 8 minutes and the coatings so obtained were smooth and uniform, with no crystal structure visible under magnification of 100 diameters. These coatings provided an excellent undercoat for paint as well as affording excellent corrosion resistancewhen covered with lanolin or a wax type rustinhibiting film. In addition, the coatings also evidenced ability to hold a lubricant for subsequent drawing operations.

The proportions of the ingredients of this concentrate may be varied from the presently preferred values stated above within the following ranges:

Units, Formula Composition, Chemical WeightXNo. of Percent by Mols Weight Phosphoric acid HzPOr 98 04 to 12) 5.0 to 15.0 Mono-ammonium phosphate NlliHzPOinns 115X( 02 0.15) 7.0 to 15.0 Zinc chloride Zn 012. 01 to 10) 1. to1().0 Zine nitrate Zn (NO: 021:0 10) 0. to 15.0 Calcium nitrate Ca(N Oz) to 50) 12. 0 to 48. 0

Amorphous zinc phosphate coatings can he obtained by spraying as well as by immersion, the chief difference in the baths being that the spray must have a lower free acid and can be run at a lower strength. For example, a spray bath needs only 10 to 20 total points but should have an acid ratio of from 15 to 50. The required low free acid maybe initially obtained by neutralizing the free acid with zinc dust, zinc oxide or calcium carbonate, sodium or ammonium hydroxides or by sodium nitrite. The resulting acid balance does not change rapidly since the baths do not hydrolyze under continuous heating. Moreover, the crystal inhibiting salts are neutral and exert a butter action to stabilize the bath against free acid formation. However, the low permissible free acid in spray formulations limits the solubility of the coating salts in the concentrate so that it is advisable to package the low acid zinc phosphate separately from the nitrate or other salt of lithium, beryllium, magnesium, calcium, strontium, cadmium, or barium to avoid recrystallization of .the ingredients.

Example IV An effective spray bath for producing an amorphous coating can be prepared from the following:

The bath was prepared by mixing the above ingredients together and with water in quantities such that the resulting solution contains 1.5% by volume of the composition designated A above and 1% by volume of that designated B, the free acid being reduced by zinc dust in an amount in the order of 0.1% by weight of the zinc concentrate A. The resulting bath analyzed 20 points, with a ratio of 25 total acid to l of free acid, and was maintained at a temperature in the order of F. At this strength and temperature an amorphous mixed phosphate coating of 200 mg. per sq. ft. was produced on ferrous metals by spraying them for 1 minute. The bath was found by analysis to contain 2 grams per liter of zinc, 6 grams per liter of phosphate and 12 grams per liter of calcium nitrate, and was held at this level by a constant drip addition of both the concentrates designatedA and B.

Tl 1e proportions of the ingredients in the concentrate employed in compounding this bath may be varied from the presently preferred values stated above within the following ranges:

Units, Formula Chemical WcightXNo. oi

Mols

Mono-ammonium phosphate N H4HP04 115X(0. 05-0. 20)

Zinc dihydrogen phosphate Zn(H2P 0 )g 261x (0. 05-0 25) Ammonium chloride N H401 53X(0. 05-0. 15) 236X(0. 10-0. 50)

Calcium nitrate Ca (N 03):.41120 A s mentioned heretofore, conventional zinc phosphate baths can-be converted'to provide an amorphous coating of a mixed phosphate and an example of how this may be accomplished has been given above. In general, it has been found that for best resultsthe nitrate or other. soluble salt of lithium, beryllium, magnesium, calcium, strone tium, cadmium or barium should be employed inan amount at least equimolar with the zinc phosphate and that an accelerating agent be used. The preferred accelerating agents are the neutralizing oxidizers such as sodium nitrite, calcium hypochlorite and barium nitrate which decompose in the bath to leave a neutralizing cation in solution after the gaseous oxidant is released.

The above specific exampleshave employed a nitrate of lithium, beryllium, magnesium, calcium, strontium, cadmium or barium as an inhibitor of crystal formation in zinc phosphating formulations and other ingredients have been included to facilitate the coating formation. Thse are not, however, inflexible requirements since any zinc phosphate coating bath can be made to produce an amorphous mixed phosphate coating bath by employing a salt of one of the abovementioned coating crystal inhibitor metals in the presence of a nitrate. Hence, it is not necessary that the nitrate of the crystal inhibitor metal be used since. a different soluble nitrate, as for example sodium nitrate, may be added if nitrate is not already present. Moreover, the nitrate may be supplied in combination with the zinc and/orthe inhibitor metal may even be employed as the phosphate thereof.

Thus, satisfactory amorphous coatings were provided by immersion of ferrous articles in baths from the following concentrates. The baths were operated at temperatures near boiling and with a total acid of 25 points and a free acid of 4:

Example V Units, Formula Concentration, 7 Chemical WeightXNo. of Percent By Mols Weight Concentrate A: v Calcium monobasic phosphate Ca(H2P 04h 252X0. 10 25. 2 Phosphoric acid HaPO 98x0. 06 6. 6 Zinc nitrate Zn (N 03) 297X0. 05 14. 8 Water to dissolve 53. 4

Concentrate B:

Calcium chloride a Chm.--" 110X0. 15 16. 5 Mono-ammonium phosphate NH4H2P04 115X0. l5 17.2 Zinc nitrate Zn (N Os)2 297X0. 07 22. 2 Phosphoric acid H PO4 98x0. 07 6. 9 Water to dissolve 37. 2

I lithium, beryllium, magnesium, calcium, strontium, cadmium or barium, which may be employed in baths formulated in accordance with this invention is not limited to the minimum or threshold values specified but ,may be increased when: additional buffering action of the added base and the accelerating action, of high nitrate concemtration are desirable. For example, in formulations for use in spray type baths, the quantity of modifiersalt' may be two or three times the threshold valuejset forth. In such a case and in other relatively high concentrations of the modifier metal, the latter may be in greater concentration' than the zinc in the modified bath andhence adjustments must be made in the bath to maintain bal-' .ance and avoid sludge. This may be effected by adding phosphoric acid in amounts to provide a pH of from 2' to 3. Excessive nitrate in the bath may be avoided by employing the chlorides of zinc, lithium, beryllium, magnesium, calcium, strontium, cadmium or barium as part of the bath components rather than supplying all of theseelements in the form of nitrate. I '1 i for forming integral amorphous phosphate coatings. Example VI A predominately iron phosphate film can be on ferrous stock by dipping it in solution of a diacidic phosphate such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogenphosphate, magnesium dihydrogen phosphate or calcium dihydrogen phosphate accelerated with an oxidizing or.re-'

ducing agent. Suitable oxidizing agents are sodium chlorate, sodium nitrite, sodium nitrate, hydrogen peroxide,

potassium persulfate, picric'acid, quinone, and various other chlorates, bromates, and iodates. Likewise, suit: able reducing agents are'sodium sulfite, sodium thiosulfate, and sodium phosphite. Thus a concentrate may be made of the following composition:

, o 7 Parts (N 4) 2 4. 75 CaCl 11 This is made up 5 percent by volume into an iron phosphating solution. This bath could be accelerated by bubbling in gaseous nitrosyl chloride or by adding aqueous nitrobetaine, or NOCl amine complexes or Roussins salts which are nitroso complexes of iron and sulfur. These are further. describedon page 678 of the Fritz Ephraims Inorganic Chemistry, 4th ed. (1943). This is an improvement to the Glen L. Williams Patent No. 1,514,494 which disclosed phosphating solutions con-2 Example VII A concentrate having the following composition by weight was used as a concentration of 5% by weight:-

. 7 Percent Manganese chloride 18 Calcium nitrate Y 42i Monosodium phosphate 26 Diglycolic acid 14' The bath was broken in to contain some iron and ferrous articles were immersed therein at about l65 ,F.

until a gunmetal grey non-crystalline coating vwas formed- This coating provided excellent properties as an undercoating to the adhesive bonding of rubber to the coated metal surface. may be substituted by other reducing agents such as sugars or glycols, aldehydes and sulfites. These reduc-.

ing agents when used with the nitrate form areduced nitrate (or nitrite) accelerator.

In a like manner when manganese and iron phosphate coatings are desired, the manganese and iron ions may 1 replace the ,zinc ions in the foregoing examples by using'. f P such chemicals as manganese dihydrogen phosphate, mono-ammonium phosphate, manganese chloride, and

ammonium chloride.

The present invention also relates to .a method of. forming adry mixture of chemicals used for. phosphate. coating baths which produceboth crystalline and'micro- In accordance'with this aspect of the invention, 'zincnitrate is ,coatedwith' crystalline coatings on the work.

zinc oxide beforemixing with other coating materials of which calcium chloride, sodium acid phosphate and an acid selected from a member'ofjthejgroup consisting P senters of diglycolic acid and sulfamic acid are to make a phosphate coating bath.

The zinc nitrate crystals'ar'e coatdiwitka crusty cement-like coating of zinc oxide byrmixiugypboutd The following example illustrates still another bath formed In Example VII, diglycolic acid,

pounds of zinc oxide with about 30 to 200 pounds of zinc nitrate or about 2 to 16% by weight of the zinc oxide based on the weight of the zinc nitrate. The adherent zinc oxide coating prevents any appreciable deliquescing action by the zinc nitrate and any subsequent reaction of the nitrate with a hydrogen atom of the acid or the sodium acid phosphate to form nitric acid. Also urea may be used with the zinc oxide at a rate of about 1 to 6% by weight of the zinc nitrate in order to prevent a reduction of the nitrate and to react with any nitrous acid fumes that might be formed by thermal decomposition of the nitrate.

The calcium chloride crystals, also being deliquescent are prevented from forming a hydrate by coating the crystals with about 2 to 16 percent by weight calcium phosphate. Calcium .oxide may also be used asthe coating material, although results are not as good since the calcium oxide itself tends to pick up some water and the sulfamic acid tends to dissolve the oxide if it becomes moist.

The zinc nitrate and calcium chloride are preferably dehydrated before applying their respective coatings. Generally, zinc nitrate or calcium chloride crystals that have been exposed to the atmosphere should be dried so as to eliminate any substantial amount of water of crystallization.

The sulfamic acid or diglycolic acid is preferably coated with starch so as to isolate the acid from the zinc oxide coating and the like which would tend to dissolve in the acid in the presence of substantial amounts of moisture. The amount of starch used as the coating agent is generally about 5 to percent by weight of the acid. The sulfamic acid is added to provide acidity to the bath as well as to reduce the amount of sludge formed. The sulfamic acid is reactive with nitrous acid and, when free to react, tends to scavenge any nitrous acid fumes that might be formed from the decomposition of nitrates.-

For best results, the materials should be intimately mixed by suitable means such as ribbon-type mixers and packaged in metal or fiber drums whichmaybe lined with polyethylene or other plastic film.

The dry mixture may be accurately weighed and easily dumped or otherwise placed in a tank of water. Generally the dry mixture is used at a rate of about A2 to percent by weight of the total bath although the best coating results are obtained at a concentration of about 4 to 8 parts by weight.

The following dry mixtures are illustrative of the present invention:

Parts by weight Zinc nitrate (coated with from about 2 to 16% by weight of zinc oxide) 20-40 Monosodium phosphate -50 Calcium chloride (coated with from 2-16 percent by weight of calcium phosphate) 10-30 Sulfamic acid (coated with from 515% by weight of starch) 2-20 The following example is for the purpose of illustration and is not intended to limit the invention in any way:

Example VIII An intimate, dry mixture of ingredients was made according to the recipe that follows:

Ingredients: Parts by weight Zinc nitrate (coated with zinc oxide at a ratio Fifty pounds of the above mixture was dumped into gallons 'of'water and stirre'd'to form an aqueous solution. The bath was maintainedat F. and iron ions were supplied to'the bathby scrap iron. Freshly pickled 'cold rolled steel panels were immersed therein for 10 minutes. The surfaces of the steel panels'were observed to have a fine, smooth, amorphous-like phosphate coating.

As previously noted and hereinafter more fully described, dififerent percentages of the different ingredients described in Example VIII, such as zinc nitrate, may be used to obtain benefits of the present invention. Calcium chloride may besubstituted for by zinc chloride, which may be given a protective coating of zinc oxide, calcium oxide or calcium phosphate. Calcium nitrate may be used in place of the zinc nitrate and other suitable means of supplying the Ca, N0 P0 Zn and Cl ions may be used as long as the ratios of Ca ion to Zn ion, Ca ion to N0 ion and N0 ion to P0 ion are maintained within the previously disclosed ranges.

Example IX A powder spray bath was made according to the following formula:

Ingredients: Parts by Weight Zinc nitrate (coated with 10% zinc oxide by weight) 33 Sodium acid phosphate (coated with 5% starch by weight) Calcium nitrate (coated with 5% calcium acid phosphate powder, known as dry sugar acid,

by weight) Twenty pounds of this powder is dumped into 100 gallons of water and stirred to form an aqueous solution. 10 pounds of calcium nitrate is added at the start of the operation to insure an amorphous coating. The bath is maintained at F. This solution is sprayed on clean steel panels by conventional spray equipment to form a smooth, amorphous coating. If desirable, the iron of the bath can be controlled by addition of sodium nitrite in amounts of 4 to 12 oz. per 100 gallons of bath. The bath is maintained at 8-12 points by addition as required.

When predominantly iron phosphate or manganese phosphate coatings are desired, other ingredients may be used such as ammonium phosphate, ammonium dihydrogen phosphate as previously more fully described.

The baths are also preferably accelerated with suitable oxidizing agents (such as sodium chlorate, sodium nitrate or sodium nitrite) or reducing agents (such as sodium sulfite or sodium thiosulfate).

While sulfamic acid is preferred as the solid acid of the dry mixture, diglycolic acid or carbamide phosphoric acid may be used although an excessive sludgiug action of the bath results from their use. Normally aqueous solutions of acids such as glycolic acid may be used, but in this case the dry material is mixed without the liquid acid. The acid is then added to the water when the bath is made up with the dry mixture.

This application is a continuation in part of my copending application Serial No. 274,839 filed March 4, 1952, now abandoned, which is a continuation-in-part of application Serial No. 193,290 filed October 31, 1950, now Reissue Patent No. 24 ,017, formerly US. Patent No. 2,588,234.

It is to be understood in accordance with the provisions of the patent statutes, the particular form of product shown and described and the particular procedure set forth are presented for purposes of explanation and illustration and that various modifications of said product and procedure can be made without departing from my invention.

Having described my invention, what I claim is:

1. A phosphate coating bath make-up compound in powder form comprising 20 to 40 parts of zinc nitrate particles having a zinc oxide coating thereon, 2 to 20 parts of acid particles selected from a member of the group consisting of diglycolic acid and sulfamic acid with a coating of starch on its particles, 30 to 50'parts of mono-basic sodium phosphate, 10 to 30 parts of calcium chloride having a coating of calcium phosphate powder on its particles so that said composition can be mixed with water to make a non-sludging phosphate coating bath.

2. A method of making a phosphate coating bath make-up compound in powder form comprising the steps of coating zinc nitrate with zinc oxide by mixing about 5 pounds of zinc oxide with about 30 to 200 pounds of zinc nitrate, coating calcium chloride with calcium phosphate by mixing With the calcium chloride about 2 to 16 percent of its Weight of calcium phosphate, and mixing said coated zinc nitrate and calcium chloride with relatively dry sulfamic acid and mono-basic sodium phosphate to form a stable dry powdery mixture.

References Cited in the file of this patent UNITED STATES PATENTS Allen Jan. 14, 1919 Romig June 21, 1938 Thompson Mar. 2, 1943 Rosenbloom Feb. 28, 1950 Tanner Mar. 14, 1950 Roland Nov. 7, 1950 Amundsen Feb. 6, 1951 Henricks Mar. 4, 1952 FOREIGN PATENTS Great Britain Dec. 23, 1935 Great Britain Jan. 18, 1940 Great Britain Jan. 17, 1951 Germany July 1, 1922 

1. A PHOSPHATE COATING BATH MAKE-UP COMPOUND IN POWDER FROM COMPRISING 20 TO 40 PARTS OF ZINC NITRATE PARTICLES HAVING A ZINC OXIDE COATING THEREON, 2 TO 20 PARTS OF ACID PARTICLES SELECTED FROM A MEMBER OF THE GROUP CONSISTING OF DIGLYCOLIC ACID AND SULFAMIC ACID WITH A COATING OF STARCH ON ITS PARTICLES, 30 TO 50 PARTS OF MONO-BASIC SODIUM PHOSPHATE, 10 TO 30 PARTS OF CALCIUM CHLORIDE HAVING A COATING OF CALCIUM PHOSPHATE POWDER ON ITS PARTICLES SO THAT SAID COMPOSITION CAN BE MIXED WITH WATER TO MAKE A NON-SLUDGING-PHOSPHATE COATING BATH. 